a) Field of the Invention
The invention relates to an optical disc and a method for fabricating the same and, more particularly, to an optical disc capable of suppressing vibration while performing read/write and a method for fabricating such optical disc.
b) Description of the Related Art
An optical disc can store data in different formats and is the most convenient storage medium among the optical storage media of the new generation. In addition, an optical disc can be applied in many fields, including library archives, data backup, electronic publication, image data storage, and personal medical record management.
Shown in FIG. 1A is the top view of a conventional optical disc 1; the conventional optical disc 1 is annular and can be divided into an inner supporting portion 11 and an outer recording portion 12. The detailed structure of the conventional optical disc 1, as shown in FIG. 1B, includes an annular substrate 13, a coated layer 14, and a compensation sheet 15. The coated layer includes a recording layer 141, a reflective layer 142, and a protective layer 143, which are sequentially laminated on the annular substrate 13, forming the recording portion 12. The compensation sheet 15 is attached to the annular substrate 13 to cover the coated layer 14, thus yielding the product of optical disc 1.
To reduce manufacturing steps and lower production cost, another conventional form of optical disc 2 as shown in FIG. 2 has been developed. The main difference between the optical disc 2 and the optical disc 1 is that the optical disc 2 does not include a compensation sheet, and since the optical disc 2 lacks the compensation sheet, the thickness of the annular substrate 21 at the supporting portion 11 is increased so that a device for driving an optical disc can clamp the optical disc 2 effectively. For example, the thickness of optical disc 2 at the supporting portion 11 is about 1.2 mm, and at the recording portion, the thickness of optical disc 2 is about 0.6 mm.
Yet another conventional form of optical disc 3 is an improvement of the optical disc 2, wherein the difference is that the supporting portion 11 protruding from the annular substrate 33 has a plurality of indentations 31 on its outer periphery, as shown in FIG. 3A. Another difference is that the supporting portion 11 protruding from the annular substrate 33 has a slant face 32 extending outward from its outer periphery, as shown in FIG. 3B. The two abovementioned characteristics allow the annular substrate 33 to be easily fabricated and to have better mechanical properties.
It is inevitable that when an optical disc is revolving in a driving device, vibration is generated due to factors including rotation of the spindle of the driving device, vibration of the pick-up head of the driving device, and air turbulence occurring in the driving device. When resonance occurs between the optical disc and any of the aforementioned vibration factors, or during high-speed read/write process, the rotating speed of the spindle of the driving device increases greatly, and the vibration generated becomes more intense. The compensation sheet that the optical disc 1 has effectively increases the rigidity of the optical disc 1, and therefore prevents the optical disc from being deformed due to vibration during the read/write process. However, the rigidity of the compensation sheet 15 would lead to warping of the optical disc if the surface quality of the compensation sheet 15 is poor, and thus affect the read/write quality of the optical disc; the warping would even render the optical disc defective. The thickness of the optical discs 2, 3 at the recording portion 12 is only 0.6 mm, and so the optical discs 2, 3 are liable to be incompatible in high-speed read/write situations because of vibration.
To conclude from above, it is important to resolve the vibration problem of optical disc during read/write process at different speeds so that the compatibility of optical discs with insufficient rigidity can be enhanced and the optical discs can be produced more easily.